Apparatus and method for acquiring a preamble in an orthogonal frequency division multiple access mobile terminal

ABSTRACT

A preamble acquisition apparatus includes a first PN code generation unit for generating a first PN code having a bit string, a first correlation calculation unit for correlating a received frequency domain preamble signal with the first PN code within a first correlation range to generate a first correlation value, a first correlation value comparison unit for comparing the first correlation value with a first threshold value, a second PN code generation unit for generating a second PN code, a second correlation calculation unit for correlating the received frequency domain preamble signal with the second PN code within a second correlation range to generate a second correlation value, and a preamble acquisition determination unit for comparing the second correlation value with a second threshold value to determine whether to acquire the preamble. The bit values of the first PN code are located in the second PN code.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/694,243, filed on Mar. 30, 2007, and claims the benefit of andpriority from Korean Patent Application No. 10-2006-0037986, filed Apr.27, 2006 which are both hereby incorporated by reference for all purposeas if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for acquiring apreamble in an orthogonal frequency division multiple access (OFDMA)mobile terminal, and more particularly, to an apparatus and method foracquiring a preamble by correlating a received preamble symbol with twotypes of pseudo-noise (PN) codes having different lengths.

2. Discussion of the Background

The portable Internet, wireless broadband (WiBro), which is in thespotlight as a substitute for third generation (3G) wireless mobilecommunication technology based on Wideband Code Division Multiple Access(WCDMA), CDMA 2000, and the like, may offer solutions to problems of thethird generation mobile communication technology, such as the limit oftransmission speed.

The portable Internet, referred to as a 3.5 generation (3.5G) mobilecommunication technology, has advantages of mobility, which is providedin the third generation wireless mobile communication, and a high datatransmission speed of broadband Internet.

The portable Internet adopts an orthogonal frequency division multipleaccess (OFDMA) system using a transmission band of about 100 MHz from afrequency band between 2.3 GHz and 2.4 GHz, and even when a user istraveling at a speed of about 60 km/hour, the portable Internet maysupport stable data transmission of more than 1 Mbps, which is differentfrom the conventional third generation mobile communication technology.Accordingly, the portable Internet may be capable of simultaneouslyproviding various types of services, and of transmitting multimedia datain real time.

OFDMA, which is a multi-access method adopted by the portable Internet,designates a system where a single channel carrier band is divided intomany sub-channel carriers, which are also referred to as subcarriers,and users are allocated to a different group of valid subcarriers.

A connection between a mobile base station and a mobile terminalaccording to the OFDMA system includes an upstream channel correspondingto data transmission from the mobile terminal to the mobile basestation, and a downstream channel corresponding to data transmissionfrom the mobile base station to the mobile terminal. An upstream channeland a downstream channel transmit data by a frame unit, which includes aplurality of symbols. Here, a first symbol of each frame corresponds toa preamble, and the preamble is used for searching a cell and forperforming base station identification and initial synchronization of aportable Internet terminal. Specifically, a cell searching process forsearching for a cell of the portable Internet terminal and identifying atarget base station with which to establish a wireless connection mayfrequently occur when supplying power to the portable Internet terminalor when performing a hand-off due to a portable Internet terminal'smovement between cells. Also, the cell searching process should beperformed quickly to ensure and maintain quality of service.

According to the Institute of Electrical and Electronics Engineers(IEEE) 802.16d/e standard, each frequency band includes 1,024subcarriers. Of these 1,024 subcarriers, 172 subcarriers are guard bandsubcarriers, and 852 subcarriers are utilized for data transmission.Each base station is allocated with a plurality of subcarriers for eachdesignated segment, and transmits a plurality of data symbols using theallocated subcarriers. Also, according to the IEEE 802.16d/e standard,each of 284 subcarriers in a group of 852 subcarriers, which areincluded in each of the frequency bands, are allocated among 3 segments.Accordingly, a single OFDMA symbol includes a bit string which istransmitted via 284 subcarriers.

FIG. 1 is a diagram illustrating a preamble transmission structure foreach segment in a frequency domain. As shown in FIG. 1, the preamble, atype of the OFDMA symbol, is transmitted via 284 subcarriers, which areregularly arranged at intervals of 3 subcarriers. In FIG. 1, only asegment number of ‘0’ is described.

A preamble signal, which is transmitted from the base station, includesa unique bit string allocated to each base station. The mobile terminalreceives the transmitted preamble signal, and compares the receivedpreamble signal with a PN code generated in the mobile terminal, andthereby identifies the unique bit string contained in the preamblesignal.

When comparing the preamble signal with the PN code, a correlation inthe frequency domain is generally used. Specifically, a frequency domainpreamble signal is correlated with a plurality of PN codes, and when acorrelation value is greater than a predetermined threshold value, a bitstring of a corresponding PN code is determined to be equal to the bitstring of the received preamble signal. The above-described process isreferred to as a preamble acquisition process.

FIG. 2 is a block diagram illustrating a conventional preambleacquisition apparatus according to the conventional art. Referring toFIG. 2, a correlation calculation unit 210 receives a preamble signal201, and correlates the received preamble signal 201 and a candidate PNcode 204. Here, the candidate PN code 204 is generated by a PN codegeneration unit 230. Also, a preamble acquisition determination unit 220compares a correlation value 202 with a predetermined threshold value,and determines whether to acquire the preamble. When the correlationvalue 202 is greater than the threshold value, the PN code 204 isacquired and outputted as an acquired preamble. When the correlationvalue 202 is less than the predetermined threshold value, another PNcode is generated by the PN code generation unit 230, and thiscorrelation process is repeated.

Even a mobile communication system according to a conventional CDMAsystem uses a method for correlating a received preamble signal and a PNcode in a terminal to identify a base station. In the case of the CDMAsystem, the length of the PN code that is used to identify the basestation is 2¹⁵ bits. According to this method, correlating the preamblesignal and the candidate PN codes generated by the terminal requires alarge number of calculations and a significant amount of time. Thismethod also consumes scarce terminal resources to acquire the preamble.Accordingly, the entire system performance may deteriorate. Also, whenthe preamble is acquired by performing a large number of calculationseach time the initial synchronization and the cell searching process areperformed, power from a battery power source, which has only a limitedpower supply, may be consumed unnecessarily.

However, a systematic correlation method may reduce a preambleacquisition time. In a systematic correlation method, a preamble signalis initially correlated with a portion of a candidate PN code. If acorrelation value is greater than a predetermined threshold value suchthat the preamble signal and the candidate PN code are determined to besufficiently similar to each other, the preamble signal is furthercorrelated with the remainder of the candidate PN code.

This systematic correlation method is referred to as a double dwellalgorithm, and is applied to a preamble acquisition apparatus includedin a CDMA mobile terminal. FIG. 3 is a block diagram illustrating thepreamble acquisition apparatus using the double dwell algorithm.

Referring to FIG. 3, a local correlation calculation unit 310 correlatesa received preamble signal 301 with a local PN code 302 corresponding toa portion of an entire PN code 305 generated by a PN code generationunit 350. When a correlation value 303 is greater than a predeterminedthreshold value, a correlation calculation is performed with respect tothe received preamble signal 301 and the length of the entire PN code305 via an entire correlation calculation unit 330. When the correlationvalue 303 acquired from the local correlation calculation unit 310 isless than the threshold value, a control signal 304 is transmitted tothe PN code generation unit 350 to generate another PN code. Anotherlocal PN code 302 corresponding to a portion of the additionallygenerated PN code is then used for a local correlation with the preamblesignal 301 in the local correlation calculation unit 310.

Also, when a correlation value 306 acquired from the entire correlationcalculation unit 330 is less than a predetermined threshold value, apreamble acquisition determination unit 340 transmits a control signal307 to the PN code generation unit 350 to generate an additional entirePN code 305 based upon the local PN code 302 having a correlation value303 that is greater than a predetermined threshold value. Theadditionally generated entire PN code 305 is correlated in the entirecorrelation calculation unit 330, and acquired if the preambleacquisition determination unit 340 determines to acquire the preamblebased on the correlation value 306.

According to the double dwell algorithm, a preamble acquisition time maybe significantly reduced by eliminating an unnecessary correlation time.However, when using the double dwell algorithm, the calculation time maybe reduced via a systematic correlation calculation, but an operation ofgenerating a PN code is not systematically performed. Accordingly, theentire PN code 305 is generated for each calculation even when the localPN code 302, which is a portion of an entire PN code 305, results in acorrelation value 303 that is less that the threshold value.

Also, a preamble acquisition apparatus using the conventional doubledwell algorithm must repeat a local correlation calculation at the localcorrelation calculation unit 310 even when a local PN code 302, which isused for the local correlation calculation, is identical to a previouslyused local PN code 302.

Ineffectiveness of the double dwell algorithm, as described above, isattributed to the property of a CDMA PN code. Specifically, the lengthof the CDMA PN code is 2 ¹⁵ bits, which is relatively long. Also, theCDMA PN code is not clearly defined in a standard of possible PN codes.Accordingly, performance of the double dwell algorithm may be improvedby improving a method of generating entire PN codes 305, andsystematically correlating a preamble signal with a portion of theentire PN codes 305.

However, in the case of the OFDMA PN code, the length of the OFDMA PNcode is 284 bits, which is comparatively very short. Also, the types ofpossible PN codes are limited to 114. Accordingly, when appropriatelyusing this feature of OFDMA PN codes, the problems which occur in thedouble dwell algorithm may be solved. Specifically, using properties ofPN codes contained in OFDMA that differ from CDMA PN code properties maypermit the improvement of performance over performance when using theconventional double dwell algorithm.

Accordingly, a new technology has been developed to improve preambleacquisition speed by applying a systematic correlation calculationmethod to an OFDMA mobile terminal, and to prevent unnecessary powerconsumption by leveraging the properties of OFDMA PN codes.

SUMMARY OF THE INVENTION

This invention provides an apparatus and method for acquiring a preamblein an OFDMA mobile terminal by correlating a received preamble symbolwith two types of pseudo-noise (PN) codes having different lengths tothereby reduce a preamble acquisition time.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

The present invention discloses an apparatus for acquiring a preamble inan orthogonal frequency division multiple access (OFDMA) mobileterminal. The apparatus includes a first PN code generation unit togenerate a first PN code comprising a bit string including at least onebit, a first correlation calculation unit to correlate a preamble signalwith the first PN code within a first correlation range to generate afirst correlation value, a first correlation value comparison unit tocompare the first correlation value with a first threshold value and todetermine whether to generate a second PN code, a second PN codegeneration unit to generate a second PN code comprising bit values ofthe first PN code, a second correlation calculation unit to correlatethe preamble signal with the second PN code within a second correlationrange to generate a second correlation value, and a preamble acquisitiondetermination unit to compare the second correlation value with a secondthreshold value.

The present invention also discloses an orthogonal frequency divisionmultiple access (OFDMA) mobile terminal apparatus including a frequencydomain transform unit to transform a time domain preamble signal into afrequency domain preamble signal, a preamble acquisition unit to acquirea preamble by correlating the frequency domain preamble signal with a PNcode, and a cell search unit to extract base station information of acell where the terminal apparatus is located from the acquired preamble.The preamble acquisition unit correlates the frequency domain preamblesignal with a first PN code within a first correlation range, andcorrelates the frequency domain preamble signal with a second PN codecomprising bit values of the first PN code within a second correlationrange to determine whether to acquire the preamble.

The present invention also discloses a method for acquiring a preamblein an orthogonal frequency division multiple access (OFDMA) mobileterminal. The method includes correlating a frequency domain preamblesignal with a first PN code within a first correlation range to generatea first correlation value, comparing the first correlation value with afirst threshold value, and determining whether to generate a second PNcode; generating a second PN code comprising bit values of the first PNcode, correlating the frequency domain preamble signal with the secondPN code within a second correlation range to generate a secondcorrelation value, and comparing the second correlation value with asecond threshold value, and acquiring the second PN code as thepreamble.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram illustrating a conventional OFDMA preambletransmission structure in a frequency domain.

FIG. 2 is a block diagram illustrating a preamble acquisition apparatusaccording to a conventional art.

FIG. 3 is a block diagram illustrating a preamble acquisition apparatususing a double dwell algorithm according to the conventional art.

FIG. 4 is a block diagram illustrating a preamble acquisition apparatusaccording to an exemplary embodiment of the present invention.

FIG. 5 illustrates an index table included in an index table storageunit of a preamble acquisition apparatus according to an exemplaryembodiment of the present invention.

FIG. 6 illustrates a code table included in a code table storage unit ofa preamble acquisition apparatus according to an exemplary embodiment ofthe present invention.

FIG. 7 is a block diagram illustrating an OFDMA mobile terminalaccording to an exemplary embodiment of the present invention.

FIG. 8 is a flowchart illustrating a method for acquiring a preambleaccording to an exemplary embodiment of the present invention.

FIG. 9 is a flowchart illustrating a method for acquiring a preambleaccording to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventionto those skilled in the art. In the drawings, the size and relativesizes of layers and regions may be exaggerated for clarity. Like numbersrefer to like elements throughout.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, the present invention will be described in detail withreference to the accompanying drawings.

FIG. 4 is a block diagram illustrating a preamble acquisition apparatusaccording to an exemplary embodiment of the present invention. Referringto FIG. 4, a first correlation calculation unit 410 correlates areceived preamble signal 401 in the frequency domain with a first PNcode 404 within a first correlation range, and generates a firstcorrelation value 402. The first PN code 404 is generated by a first PNcode generation unit 430. The first correlation value 402 is inputtedinto a first correlation value comparison unit 420, and compared with afirst threshold value. Whether the received preamble signal 401 iscorrelated with a second PN code 407 depends upon the result of thiscomparison.

Specifically, according to an exemplary embodiment of the presentinvention, if the first correlation value 402 is greater than the firstthreshold value, the received preamble signal 401 is correlated with thesecond PN code 407, which is generated by a second PN code generationunit 460, within a predetermined second correlation range. To thecontrary, if the first correlation value 402 is less than the firstthreshold value, the first correlation value comparison unit 420transmits a first control signal 403 to the first PN code generationunit 430 to generate an additional first PN code 404.

If the first correlation value comparison unit 420 determines that thereceived preamble signal 401 should be correlated with the second PNcode 407 in a second correlation calculation unit 440, the second PNcode generation unit 460 generates the second PN code 407 where a codeidentical to the first PN code 404 is located in specific bits of thesecond PN code 407. Also, the second correlation calculation unit 440correlates the preamble signal 401 with the generated second PN code 407within the second correlation range.

A second correlation value 405, which is acquired in the secondcorrelation calculation unit 440, is inputted into a preambleacquisition determination unit 450. The preamble acquisitiondetermination unit 450 compares the second correlation value 405 with asecond threshold value, and determines whether to acquire the preamble.

Specifically, according to an exemplary embodiment of the presentinvention, if the second correlation value 405 is greater than thesecond threshold value, the second PN code 407, which is used forcalculating the second correlation value 405, is acquired as thepreamble. To the contrary, if the second correlation value 405 is lessthan the second threshold value, the preamble acquisition determinationunit 450 transmits a second control signal 406 to the second PN codegeneration unit 460, to generate an additional second PN code 407.

As described above, the preamble acquisition apparatus according to thepresent invention may significantly reduce an unnecessary correlationcalculation by separating a process of correlating a preamble signalwith candidate PN codes into at least two operations, and by using apre-processing procedure. In the pre-processing procedure, a first PNcode 404 with a low preamble acquisition probability is filtered via afirst correlation calculation unit 410, before a second correlationcalculation unit 440 performs a more accurate correlation calculation.Also, according to the present invention, power consumption by a mobileterminal may be reduced and quick cell searching may be supported duringa hand-off.

The operation of each configuration element shown in FIG. 4 will bedescribed in further detail below.

As described above, the first correlation calculation unit 410correlates the received preamble signal 401 with the first PN code 404within the first correlation range, and generates the first correlationvalue 402. The length of the first PN code 404 may be shorter than theentire received preamble signal 401. In this case, the length of thefirst correlation range where the entire received preamble signal 401and the first PN code 404 are correlated may be identical to the lengthof the first PN code 404.

Also, the first correlation range may have the same length as the firstPN code 404 where a specific bit of the preamble signal 401 is astarting location. Also, the second correlation range for the secondcorrelation calculation unit 440 to correlate the preamble signal 401with the second PN code 407 may have the same length as the second PNcode 407, which is generated by the second PN code generation unit 460.

According to an exemplary embodiment of the present invention, thelength of the first correlation range may be shorter than the length ofthe second correlation range. For example, the length of the firstcorrelation range may be 4 bits. Also, the length of the secondcorrelation range may be determined to have a value less than a numberof subcarriers, and more specifically, less than the length of areceived preamble signal 401.

In an OFDMA mobile communication system, a single preamble signalincludes a unique bit string of 284 bits. The preamble signal mayinclude a single bit string among different bit strings for a total of114 bits. Since each single subcarrier is allocated to each bit, thesingle preamble signal is transmitted via 284 subcarriers. Accordingly,the length of the second PN code and the second correlation range maynot exceed 284 bits. Also, according to the above-described exemplaryembodiment, the length of the first correlation range may be shorterthan 284 bits.

Hereinafter, this exemplary embodiment will be described where thelength of the first correlation range is four bits and the length of thesecond correlation range is 284 bits. Also, although the firstcorrelation range may start from a specific location of the preamblesignal, this exemplary embodiment will be described where the firstcorrelation range corresponds to the first four bits of the preamblesignal. It will be apparent to those of ordinary skill in the relatedart that the present invention is not limited thereto.

Referring again to FIG. 4, the first PN code 404 is generated by thefirst PN code generation unit 430, and may have a length of four bits.In this circumstance, a total of 16 (=2⁴) unique codes may exist. Thesemay be referred to as possible first PN codes, and may depend upon thenumber of bits of the first PN code. Each first PN code 404 may beindicated by a hexadecimal.

Accordingly, the first correlation calculation unit 410 performs a totalof 16 correlation calculations with respect to the received preamblesignal 401 within the 4-bit correlation range. If the first PN code 404has a greater correlation value than the first threshold value among thefirst correlation values 402 according to the comparison result of thefirst correlation value comparison unit 420. The first PN code 404 alsohas a comparatively similar value to the first four bits of the preamblesignal 401. Accordingly, the first PN code 404 may also be used for acorrelation calculation with the second PN code 407 having, for example,284 bits, which is equal to the number of subcarriers of the preamblesignal 401 and greater than the first PN code 404. Conversely, when thefirst correlation value 402 is less than the first threshold value, thesecond PN code 407 corresponding to the first PN code 404 is notgenerated for the correlation calculation in the second correlationcalculation unit 440.

Specifically, the second PN code 407 may be determined so that a bitstring of a pattern identical or similar to the first PN code 404 islocated in specific bits of the second PN code 407. Accordingly, thesingle second PN code 407 corresponds to the single first PN code 404.Also, the single first PN code 404 may correspond to at least one secondPN code 407.

Accordingly, when the first correlation value comparison unit 420determines that the received preamble signal 401 should be correlatedwith the second PN code 407, the second PN code generation unit 460 maygenerate the second PN code 407 with the length of 284 bits by referringto a corresponding relation between the first PN code 404 and the secondPN code 407 as described above.

For example, the first correlation value 402 is acquired by correlatingthe first four bits of the received preamble signal 401 and the first PNcode 404 having a binary “0000” value, i.e. a hexadecimal ‘0’ value, andwhen the first correlation value 402 is greater than the first thresholdvalue, the second PN code generation unit 460 generates only second PNcodes 407 that start with the hexadecimal ‘0’ value, from a total of 114possible second PN codes 407 having a length of 284 bits. The second PNcode generation unit 460 then inputs the generated second PN codes 407into the second correlation calculation unit 440.

Hereinafter, an operation of the second PN code generation unit 460generating a second PN code 407 from the first PN code 404 will bedescribed in detail.

According to an exemplary embodiment of the present invention, thesecond PN code generation unit 460 may include an index table storageunit and a code generator. The index table storage unit stores an indexof a second PN code 407 corresponding to a first PN code 404. The codegenerator generates the second PN code 407 based on an index value ofthe second PN code 407.

FIG. 5 illustrates an example of an index table according to theabove-described exemplary embodiment. Referring to FIG. 5, an index ofthe second PN code 407 corresponding to each of 16 first PN codes isstored in a form of a table. Specifically, indexes of second PN codes407 which start with the hexadecimal ‘0’ may be 37, 42, 52, 54, 89, 86,and 101.

Accordingly, the code generator may generate the second PN code 407based on the index value of the second PN code 407 that is stored in theindex table storage unit.

For example, the code generator may be a PN code generator that includesa series of shift registers, and may generate the second PN code 407,which consists of a total of 284 bit strings, by using the index of thesecond PN code 407 as a seed or an initial input pattern.

As described above, in the case of a PN code which is used foridentifying an OFDMA preamble, a limited number of code patterns may bedefined according to a standard. Accordingly, it is possible topre-store the corresponding relation in the form of the table and referto the table when performing the correlation calculation. However, thelength of a CDMA PN code using a double dwell algorithm is relativelyvery long and a code pattern thereof is not pre-defined. Accordingly,the CDMA PN code may not configure the preamble acquisition apparatus asdescribed in the present exemplary embodiment. Thus, according to thepresent exemplary embodiment where the property of an OFDMA PN code issufficiently used, it is possible to effectively prevent a repeatedlocal correlation calculation that occurs in the conventional doubledwell algorithm.

Also, according to another exemplary embodiment of the presentinvention, the second PN code generation unit 460 may include a codetable storage unit and a code generator. The code table storage unit maystore a PN code corresponding to the first PN code 404. The codegenerator may generate the second PN code 407 by selecting the stored PNcode with reference to the code table storage unit.

FIG. 6 illustrates an example of a code table according to theabove-described exemplary embodiment. Referring to FIG. 6, a PN codecorresponding to each first PN code 404 is stored in a form of a table.The length of the stored PN code may be, for example, 284 bits, which isidentical to the length of the entire preamble signal.

Accordingly, the code generator may generate the second PN code 407 byselecting and outputting a PN code corresponding to the first PN code404 with reference to the code table storage unit as shown in FIG. 6.

Here, PN code indexes as shown in FIG. 6 are only an example forconvenience of description, and are not necessarily required toimplement the present invention, and the present invention is also notlimited thereto.

The present exemplary embodiment may include an additional memorystorage space for storing PN codes, which is different from theabove-described exemplary embodiments. However, unlike the CDMA PN code,the length of the OFDMA PN code is limited to 284 bits, and the numberof the OFDMA PN codes is limited to 114. Accordingly, PN codes may bestored in the memory space of about 30 kilobits, which can be easilyconfigured.

Also, when sharing a portion of the memory space and storing PN codes inthe shared memory space, a shift register and other calculation logicsfor generating the PN code may not be required. Also, the PN code may begenerated by referring to the memory once. Accordingly, the timerequired to generate the PN code may be reduced.

As described above, it is possible to secure further improvedperformance over the double dwell algorithm, which is applied to theCDMA PN code, by simplifying the process of generating the second PNcode.

Like the second PN code generation unit 460, the first PN codegeneration unit 430 may pre-store a total of 16 first PN codes 404, andmay use the same for the correlation calculation within the firstcorrelation range. Specifically, the first PN code generation unit 430according to the present exemplary embodiment may include a code tablestorage unit, and a code generator. The code table storage unit maygenerate and store PN codes, and the code generator may generate thefirst PN code 404 by sequentially selecting the stored PN code from thecode table storage unit.

Since the first PN code 404 may be one of 16 bit strings with the lengthof 4 bits, the first PN code 404 may be stored more easily than thesecond PN code 407. The configuration of the first PN code generationunit 430 described above may improve performance by having asubstantially similar configuration as the second PN code generationunit 460 according to the above-described exemplary embodiment.

Hereinafter, the first correlation value comparison unit 420 and thepreamble acquisition determination unit 450 will be described. While thefirst correlation value comparison unit 420 compares the firstcorrelation value with the first threshold value, the preambleacquisition determination unit 450 compares the second correlation valuewith the second threshold value. Except for the above described case,the first correlation value comparison unit 420 and the preambleacquisition determination unit 450 may be configured by using asubstantially similar method.

According to an exemplary embodiment of the present invention, the firstthreshold value which is used by the first correlation value comparisonunit 420, or the second threshold value which is used by the preambleacquisition determination unit 450, may be determined based on at leastone of a number of subcarriers transmitting the received preamble signal401, the length of the first correlation range, the length of the secondcorrelation range, a total number of the first PN codes 404, and a totalnumber of the second PN codes 407.

In this instance, the preamble acquisition apparatus may be deliveredwith the first threshold value or the second threshold value beingpre-configured. Also, the first threshold value or the second thresholdvalue may be configured by a user, or may be configured based on aparameter value calculated during the operation of the preambleacquisition apparatus.

Specifically, the preamble acquisition apparatus according to anexemplary embodiment of the present invention may include a parameterconfiguration unit. The parameter configuration unit may configure aparameter value associated with at least one of the first thresholdvalue, the second threshold value, the length of the first correlationrange, and the length of the second correlation range. Also, theparameter configuration unit may perform the configuration based on aparameter value which is inputted from a user, or based on a parametervalue calculated in association with a property of the wireless channelthat transmits the preamble.

Also, the preamble acquisition apparatus according to the presentexemplary embodiment may include a predetermined parameter calculationunit to calculate a parameter value in association with the property ofa wireless channel. The parameter calculation unit may include asemiconductor circuit for calculating a parameter, or a microprocessor,a digital signal processing unit, and other calculation units, which areincluded in the OFDMA mobile terminal having the preamble acquisitionapparatus.

FIG. 7 is a block diagram illustrating an OFDMA mobile terminalaccording to an exemplary embodiment of the present invention. The OFDMAmobile terminal includes a frequency domain transform unit 710, apreamble acquisition unit 720, and a cell searching unit 730.

Hereinafter, the elements of the OFDMA mobile terminal according to thepresent exemplary embodiment will be described in detail.

A preamble signal transmitted via a wireless channel and received at awireless terminal may be a time domain signal 701, and may betransformed into a frequency domain signal to acquire a preambleaccording to the present exemplary embodiment. Accordingly, thefrequency domain transform unit 710 transforms a time domain preamblesignal 701 into a frequency domain preamble signal 702. For example, thefrequency domain transform unit 710 may include a fast Fourier transform(FFT). Also, the frequency domain transform unit 710 may be widelyapplied even to other units which can transform the time domain signal701 into the frequency domain signal 702.

Also, the preamble acquisition unit 720 systematically correlates atransformed frequency domain preamble signal 702 with a first PN code404 and a second PN code 407, which are generated in the OFDMA mobileterminal, according to the present exemplary embodiment.

Specifically, the preamble acquisition unit 720 correlates thetransformed frequency domain preamble signal 702 with the first PN codewithin a first correlation range, and according to the correlationresult, correlates the frequency domain preamble signal 702 with thesecond PN code within a second correlation range, and thereby,determines whether to acquire a preamble 703. The second PN codeincludes a code identical or substantially similar to the first PN codein specific bits of the second PN code.

More specifically, the length of the first PN code and the firstcorrelation range may be shorter than the length of the second PN codeand the second correlation range. The first

PN code may have the length of four bits. Also, the length of the secondPN code may be a value no longer than the length of the entire preamblesignal 702.

The preamble 703, which is acquired via the systematic correlationcalculation, is inputted into the cell searching unit 730, and the cellsearching unit 730 may extract base station information of a cell wherethe OFDMA mobile terminal is located, from the preamble 703 according tothe present exemplary embodiment.

The base station of an OFDMA mobile communication system transmits thepreamble 703 to each mobile terminal by using a group of subcarriers ofa segment. The preamble includes a unique bit string which is assignedto the base station. Accordingly, the OFDMA mobile terminal may performcell searching by extracting the base station information of the cellwhere the terminal is located using the bit string. Here, the bit stringis included in the preamble 703 acquired by the preamble acquisitionunit 720.

The present invention may be applied to a method of acquiring a preamblefrom a received preamble signal in an OFDMA mobile terminal. FIG. 8 is aflowchart illustrating a method of acquiring a preamble according to anexemplary embodiment of the present invention. Hereinafter, the preambleacquisition method will be described in detail with reference to FIG. 8.

In operation S810, the preamble acquisition method correlates a receivedfrequency domain preamble signal with a first PN code within a firstcorrelation range, and generates a first correlation value. The lengthof the first PN code and the first correlation range may be shorter thanthe length of the entire preamble signal, and may be four bits forexample.

In operation S820, the preamble acquisition method compares the firstcorrelation value with a first threshold value, and determines whetherto generate a second PN code corresponding to the first PN code. Thefirst threshold value may be determined based on at least one of anumber of subcarriers transmitting the preamble, the length of the firstcorrelation range, the length of the second correlation range, a totalpossible number of first PN codes, and a total possible number of secondPN codes.

In operation S830, the preamble acquisition method generates the secondPN code corresponding to the first PN code according to the result fromoperation S820. In this case, the second PN code is generated so that acode substantially similar to or identical to the first PN code islocated in specific bits of the second PN code. The length of the secondPN code may be longer than the length of the first PN code, and may beno longer than the length of the entire received preamble signal. Inparticular, the second PN code may include an equal number of bitstrings as the total number of subcarriers which are used fortransmitting the preamble.

In operation S840, the preamble acquisition method correlates thereceived frequency domain preamble signal with the second PN code withina second correlation range, and generates a second correlation value.The length of the second correlation range may be equal to the length ofthe second PN code.

In operation S850, the preamble acquisition method compares the secondcorrelation value with a second threshold value, and acquires the secondPN code as the preamble according to the comparison result.

FIG. 9 is a flowchart illustrating a method of acquiring a preambleaccording to another exemplary embodiment of the present invention.Operations S810, S830, and S840 shown in FIG. 9 are substantiallysimilar to operations S810, S830, and S840 described with respect toFIG. 8. Thus, a detailed description thereof will be omitted.

FIG. 9 illustrates operations S820 and S850 for a method of acquiring apreamble according to an exemplary embodiment of the present inventionin further detail.

As shown in FIG. 9, operation S820 of comparing the first correlationvalue with the first threshold value and determining whether to generatea second PN code corresponding to the first PN code may includeoperation S821 and operation S822. In operation S821, the preambleacquisition method generates the second PN code corresponding to thefirst PN code when the first correlation value is greater than the firstthreshold value. In operation S822, the preamble acquisition methodrepeats operation S810 when the first correlation value is less than thefirst threshold value.

Also, operation S850 of acquiring the second PN code as the preamble mayinclude operation S851 and operation S852. In operation S852, thepreamble acquisition method repeats operation S830 of generating thesecond PN code and operation S840 of generating the second correlationvalue. In operation S851, the preamble acquisition method acquires thesecond PN code as the preamble when the second correlation value isgreater than the second threshold value.

As shown in FIG. 9, when the first correlation value generated inoperation S810 is less than a predetermined value, operation S840, whichincludes more calculations than operation S810, is not performed.Accordingly, it is possible to prevent unnecessary calculations frombeing performed for a PN code with a low preamble acquisitionprobability. Also, a preamble acquisition time in a mobile terminal maybe reduced, which may significantly improve cell searching speed andperformance.

Also, unlike the conventional double dwell algorithm, the preambleacquisition apparatus according to the present invention may perform atotal of 16 correlation calculations with respect to the receivedpreamble signal where the first PN code has four bits. Accordingly, acalculation burden of the first correlation calculation unit may begreatly decreased.

However, the conventional double dwell algorithm performs a localcorrelation calculation for local codes included in all PN codes since agroup of PN codes is not clearly defined according to CDMA standards.

As described above, according to the present invention, an apparatus andmethod are provided that can overcome disadvantages of the double dwellalgorithm as applied to the conventional CDMA PN code, and can leverageadvantages of the double dwell algorithm by using properties of theOFDMA PN code, and thereby can acquire a preamble in a more suitablemanner for OFDMA.

The method for acquiring a preamble and a mobile terminal with apreamble acquisition function according to another exemplary embodimentof the present invention has been described. Description for FIG. 4,FIG. 5, and FIG. 6 may be applicable to the present exemplaryembodiment. Thus, further detailed description related thereto will beomitted.

The term “mobile terminal” used throughout the present specification mayinclude communication devices, such as an orthogonal frequency divisionmultiplexing (OFDM) and OFDMA communication device; portable terminalssuch as a personal digital assistant (PDA), a hand-held PC, a notebookcomputer, a laptop computer, a WiBro terminal, an MP3 player, and an MDplayer; and all types of hand-held based wireless communication devices.Also, the “mobile terminal” may include a predetermined communicationmodule such as an OFDMA module, a CDMA module, a Bluetooth module, anInfrared Data Association (IrDA) module, a wired/wireless local areanetwork (LAN) card and a wireless communication device having a globalpositioning system (GPS) chip to enable tracking of a position via GPS.Also, the “mobile terminal” may include a microprocessor that can playmultimedia and perform a certain calculation operation.

The preamble acquisition method according to the above-describedembodiment of the present invention may be recorded in computer-readablemedia including program instructions to implement various operationsembodied by a computer. The media may also include, alone or incombination with the program instructions, data files, data structures,and the like. Examples of computer-readable media include magnetic mediasuch as hard disks, floppy disks, and magnetic tape; optical media suchas CD-ROM disks and DVD; magneto-optical media such as optical disks;and hardware devices that are specially configured to store and performprogram instructions, such as read-only memory (ROM), random accessmemory (RAM), flash memory, and the like. The media may also be atransmission medium such as optical or metallic lines, wave guides, andthe like, including a carrier wave transmitting signals specifying theprogram instructions, data structures, and the like. Examples of programinstructions include both machine code, such as produced by a compiler,and files containing higher level code that may be executed by thecomputer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations of the above-described embodiments of the presentinvention.

As described above, a method and apparatus for acquiring a preambleaccording to the present invention may simplify a preamble acquisitionprocess via a pre-processing procedure using a portion of PN codes, andthereby reduce a preamble acquisition time. Here, the PN codes are usedfor a preamble carrier modulation.

Also, according to the present invention, it is possible to prevent acorrelation calculation from being repeated during a pre-processingprocedure using a portion of PN codes where some patterns of the PNcodes are identical.

Also, according to the present invention, it is possible to efficientlyuse the entire resources of a terminal by reducing hardware and softwareresources used for acquiring a preamble.

Also, according to the present invention, it is possible to preventrepeating an unnecessary calculation with respect to a PN code with alow preamble acquisition probability, and to thereby more preciselyverify PN codes with a high preamble acquisition probability.

Also, according to the present invention, it is possible to store aportion of or all PN codes in a terminal since the length and a numberof PN codes, which are used for acquiring an OFDMA preamble, arelimited, and to thereby reduce a preamble acquisition time.

Also, according to the present invention, it is possible to enablethreshold values used for a two-step correlation calculation and thelength of a correlation range to be adjusted by a user or according to achannel status, and to adaptively control a preamble acquisitionperformance.

Also, according to the present invention, it is possible to improveperformance of a cell searching process that occurs during a hand-off ofan OFDMA mobile, and to prevent unnecessary power consumption by theterminal when identifying a base station in the cell searching process.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An apparatus to acquire a preamble in an orthogonal frequencydivision multiple access (OFDMA) mobile terminal, the apparatuscomprising: a first pseudo-noise (PN) code generation unit to generate afirst PN code comprising a bit string including at least one bit; afirst correlation calculation unit to correlate a received preamblesignal with the first PN code within a first correlation range togenerate a first correlation value; a first correlation value comparisonunit to compare the first correlation value with a first threshold valueand to determine whether to generate a second PN code; a second PN codegeneration unit to generate a second PN code according to thedetermination result; a second correlation calculation unit to correlatethe preamble signal with the second PN code to generate a secondcorrelation value; and a preamble acquisition determination unit tocompare the second correlation value with a second threshold value andto determine whether to acquire the preamble.
 2. The apparatus of claim1, wherein the second correlation calculation unit correlates thepreamble signal with the second PN code within a second correlationrange.
 3. The apparatus of claim 1, wherein the second PN codegeneration unit comprises: an index table storage unit to store an indexvalue of the second PN code corresponding to the first PN code; and acode generator to generate the second PN code based on the index valueof the second PN code.
 4. The apparatus of claim 1, wherein the secondPN code generation unit comprises: a code table storage unit to store astored PN code corresponding to the first PN code; and a code generatorto generate the second PN code by selecting the stored PN code from thecode table storage unit.
 5. The apparatus of claim 1, wherein the firstPN code generation unit comprises: a code table storage unit to store aplurality of PN codes; and a code generator to generate the first PNcode by selecting a stored PN code from the code table storage unit. 6.The apparatus of claim 1, wherein a bit length of the first correlationrange is less than a bit length of a second correlation range.
 7. Theapparatus of claim 1, wherein a bit length of the first correlationrange is four bits.
 8. The apparatus of claim 1, wherein a bit length ofa second correlation range is no longer than a number of subcarrierstransmitting the preamble.
 9. The apparatus of claim 1, wherein thefirst threshold value or the second threshold value is determined basedon at least one of a number of subcarriers transmitting the preamble, abit length of the first correlation range, a bit length of a secondcorrelation range, a number of possible first PN codes, and a number ofpossible second PN codes.
 10. The apparatus of claim 1, furthercomprising: a parameter configuration unit to configure a parametervalue associated with at least one of the first threshold value, thesecond threshold value, a bit length of the first correlation range, anda bit length of a second correlation range, wherein the parameterconfiguration unit configures the parameter value based on an input froma user or a property of a wireless channel transmitting the preamblesignal.
 11. An orthogonal frequency division multiple access (OFDMA)mobile terminal apparatus, comprising: a frequency domain transform unitto transform a time domain preamble signal into a frequency domainpreamble signal; a preamble acquisition unit to acquire a preamble bycorrelating the transformed frequency domain preamble signal with a PNcode; and a cell search unit to extract base station information of acell where the mobile terminal apparatus is located from the acquiredpreamble, wherein the preamble acquisition unit correlates thetransformed frequency domain preamble signal with a first PN code withina first correlation range to generate a first correlation value,determines whether to generate a second PN code according to the firstcorrelation value, and correlates the transformed frequency domainpreamble signal with the second PN code to determine whether to acquirethe preamble.
 12. The OFDMA mobile terminal apparatus of claim 11,wherein the preamble acquisition unit correlates the transformedfrequency domain preamble signal with the second PN code within a secondcorrelation range.
 13. A method for acquiring a preamble in anorthogonal frequency division multiple access (OFDMA) mobile terminal,comprising: correlating a received preamble signal with a first PN codewithin a first correlation range to generate a first correlation value;comparing the first correlation value with a first threshold value, anddetermining whether to generate a second PN code according to thecomparison result; generating a second PN code according to thedetermination result; correlating the preamble signal with the second PNcode to generate a second correlation value; and comparing the secondcorrelation value with a second threshold value, and acquiring thesecond PN code as the preamble according to the comparison result. 14.The method of claim 13, wherein correlating the preamble signal with thesecond PN code further comprises correlating the preamble signal withthe second PN code within a second correlation range.
 15. The method ofclaim 13, wherein generating the second PN code further comprises:generating the second PN code if the first correlation value is greaterthan the first threshold value; and correlating the preamble signal witha new first PN code within the first correlation range to generate a newfirst correlation value if the first correlation value is less than thefirst threshold value.
 16. The method of claim 13, wherein the acquiringthe second PN code as the preamble further comprises: generating a newsecond PN code comprising bit values of the first PN code andcorrelating the preamble signal with the new second PN code within asecond correlation range to generate a new second correlation value ifthe second correlation value is less than the second threshold value;and acquiring the second PN code as the preamble if the secondcorrelation value is greater than the second threshold value.
 17. Themethod of claim 13, wherein a bit length of the first correlation rangeis less than a bit length of a second correlation range.
 18. The methodof claim 13, wherein a bit length of the first correlation range is fourbits.
 19. The method of claim 13, wherein a bit length of a secondcorrelation range is no longer than a number of subcarriers transmittingthe preamble.